Oil spills have occurred with increasing frequency as the growing demand for petroleum products has been met by increased shipments of oil in ocean going tankers, barge traffic and the like. Oil spills caused by navigational errors, especially in the presence of rough weather and other factors, can cause devastating damage to the environment.
Much of the effort to cleanup such spills has centered on mechanical methods to contain and remove the spilled oil and to clean oil contaminated areas. However, these methods are not entirely satisfactory because much of the oil either cannot be contained or escapes containment. Even when contained, mechanical removal is at best only partial. In all oil spills, small amounts to the vast majority of the spilled oil remains in the affected areas after all best efforts to clean and remove the oil are completed.
It has long been known that oil is continuously being released into the environment by natural petroleum seeps. The quantity of oil released by these natural seeps world wide annually exceeds the sum total of all worldwide petroleum hydrocarbon releases from all other sources (i.e., oil spills, tanker washings, run-off, etc.). It is also well known that these large natural releases of petroleum do not accumulate in the environment nor cause damage to the world's ecosystem. The reasons for this is that within the earth's ecosystem there is a well established, highly diverse and ubiquitously distributed population of microorganisms that degrade petroleum hydrocarbons. The application of this knowledge to utilize petroleum degrading microorganisms to treat spilled oil is known collectively as the process or method of bioremediation.
The success or effectiveness of bioremediation is dependent upon key factors being simultaneously present. First, the presence of hydrocarbon degrading microorganisms, either naturally or by addition. Second, there must be oxygen and water available to permit the microorganisms to be metabolically active. Third, there must also be available sufficient quantities of biologically utilizable nitrogen and phosphorous to enable the microbial population to rapidly metabolize the available petroleum hydrocarbons.
Microorganisms capable of degrading petroleum hydrocarbons can be found in almost all natural bodies of water. The exact type of microorganisms present in a given area of a spill may vary greatly yet each has the ability to degrade oil. The elemental nutrient requirements of petroleum degrading microbes are approximately the same as the microbes' average elemental composition. The carbon, which makes up 48 percent of the microbes composition, is obtained from the petroleum oil slick--lights to crude in weight; C.sub.7 to C.sub.80 tars. However, the remaining elemental materials necessary to grow must be provided from either the surrounding water or a supplementary source. If the supply of these other nutrients, especially nitrogen, phosphorous, sulfur, magnesium, potassium, calcium and sodium, are exhausted, then the microbe population will not grow any further. When significant quantities of petroleum have been spilled in a body of water, essential nutrients must be applied to the petroleum to sustain microbial growth.
It is usually insufficient quantities of microbially available nitrogen and phosphorous that limit the rate of natural biodegradation of spilled oil in the environment. However, the application of water soluble nitrogen and phosphorous to spills in aquatic environments has proven to be ineffective because the nutrients are rapidly dissipated into the surrounding water volume. Nutrient additive formulations have typically suffered from a number of problems including incomplete partitioning of the nutrients into the oil phase, poor biodegradability of encapsulating materials and the difficulty and high cost of manufacturing.
In U.S. Pat. No. 3,883,397, Townsky discloses a particulate material made of a nutrient formulation coated with a lipophilic material which suspends the material in the oil or near the oil-water interface. This coating is composed of magnesium, aluminum and calcium salts of lipophilic fatty acids, specifically magnesium stearate.
It would be desirable to have a composition that would retain essential microbial available nutrients, such as nitrogen, phosphorous and iron, within the oil phase of an oil and water mixture as occurs in an oil spill in an aquatic or wetland environment. It would also be desirable for the nutrient formulation to be able to sustain growth of microorganisms throughout the body of oil. Also it would be desirable for the nutrient formulation to be supplemented with oxygen releasing compounds to provide molecular oxygen within the oil matrix to enhance growth of aerobic microorganisms. It would further be desirable if the nutrients and oxygen releasing compounds were released and/or activated at a slow and controlled rate based upon biological demands of the microorganisms through degradation of the encapsulating coating and partial dissolution of the coating into the oil phase.